Captain Lieutenant (Grose 1811 Dictionary)

Captain Lieutenant

Meat between veal and beef, the
flesh of an old calf; a military simile, drawn from the
officer of that denomination, who has only the pay of a
lieutenant, with the rank of captain; and so is not entirely
one or the other, but between both.

Definition taken from
The 1811 Dictionary of the Vulgar Tongue,
originally by Francis Grose.